The submarine takes about two hours to reach its depth of about 14,800 feet and will spend 16 hours underwater before rising. But it can only report when it surfaces, so will effectively provide a daily snapshot of the ocean floor. Scanning the area could take from six weeks to two months.

"We haven't had a single detection in six days,” said Mr Houston. “So I guess it's time to go underwater.”

The deployment of the submarine follows the detection of four sets of signals believed to be from the black box beacon. Two sets of signals were heard on March 5 and two further sets on March 7; all were detected by a beacon locator being towed by Australia’s Ocean Shield vessel.

Mr Houston, a former Australian defence chief, said it would take “a number of days” to take the oil sample ashore and test it.

"At the moment this is really all we've got," he said.

"We've got no visual objects; the only thing we have left at this stage is the four transmissions and an oil slick in the same vicinity. We will investigate those to their conclusion… The oil slick is approximately 5,500 metres down-wind and down-sea from the vicinity of the detections picked up by the towed pinger locator on Ocean Shield.”

Despite an ongoing air and search, authorities do not believe any floating wreckage from the plane will be found. Eleven military aircraft, one civilian jet and fifteen ships were searching an area spanning about 18,000 square miles.

"The chances of any floating material being recovered have greatly diminished and it will be appropriate to confer with Australia's partners to decide the way ahead later this week," Mr Houston said.

“The deployment of the autonomous underwater vehicle has the potential to take us a further step towards visual identification since it offers a possible opportunity to detect debris from the aircraft on the ocean floor.”